Weather News

/Weather News
7 11, 2018

Here comes the cool change!

After 5 days of relentless well above average heat, the strongest heatwave for November in over 2 decades for SEQLD, the cool change is FINALLY on its way! Above image showing the change circled in blue, with the cooler South and South West winds marked in purple via BSCH.

 

Since Saturday until today (Wednesday), large parts of Inland QLD and the South East corner of the State have been under a relentless heatwave. A heatwave that has seen several locations break 20+ year old streaks for November standards along with some November records being challenged and broken. While the Coastal strip in SEQLD wasn’t so bad, it had the added influence of high humidity… making the days just as uncomfortable as those areas further Inland that saw the very high temperatures.

Some of the streaks and records that were achieved include.
*Gatton recorded 3 straight days above 39ºc and 4 straight days above 37ºc+, the first time for both in November since 1996 (22 years)
*Toowoomba recorded back to back 35ºc+ days for the first time in November since 1996 (22 years)
*Ipswich recorded 4 straight 36ºc+ days for the first time in November since 1996 (22 years)
*Warwick recorded 4 straight 35ºc+ days for the first time in November since 2009 (9 years)
*Miles, Stanthorpe, Dalby, Oakey, Kingaroy, Gympie, all recorded their hottest November streaks since 2014 (4 years)
*Ballera recorded 5 straight days above 41ºc for the first time in November since 2012 (6 years)

From a records point of view,
*Ipswich recorded its hottest November night on record with 23.8ºc (records dating back to 1941)
*Charleville 29.4ºc & St George 28.6ºc had their warmest nights since 1965 for November, the second warmest night ever for Charleville in November (0.2ºc short of the 1965 record)
*Windorah recorded a very warm 31.7ºc night
*Birdsville recorded a 31.1ºc night
*Several towns recorded 28ºc+ nights across Southern Inland, Central Inland, North West, South West and Western QLD at some stage, with any other nights during the heat period being 25ºc+

The change is already being seen through South West QLD where today Birdsville maxed at just 22.1ºc and Ballera 22.4ºc – a massive 19ºc colder than yesterday! The current temperature in Ballera is a mere 15.7ºc, thats 22ºc colder than this time yesterday as well.

Forecast maximums cross Southern and SE QLD tomorrow (Thursday) via BSCH / OCF

 

While temperatures will remain near average tomorrow (Thursday) across South East QLD, the humidity will be taken way out of the equation so it will feel very comfortable. Tonight will remain fairly warm due to cloud coverage trapping some of the heat in, but the cool change should still move through and bring with it much drier South to South Westerly winds which will cut the humidity out of the air and make it actually feel quite pleasant. Across Inland areas it should be much cooler tonight, with temperatures dropping into the low teens. This should transition into a much colder day tomorrow (something similar to what SW QLD saw today) (see image above).

Forecast minimums via OCF / BSCH for Wednesday night into Thursday morning

 

11 10, 2018

Life Threatening Hurricane Michael nearing landfall!

Major Hurricane Michael is nearing its expected landfall area of the Florida Panhandle, near Panama City as a life threatening, high end Category 4, almost Category 5 system! Above image via RAMMB / CIRA.

 

Hurricane Michael developed several days ago near the Yucatan Peninsula and global models have forecast the track of the system very well, with early indications showing the system was expected to make a quick landfall over the Florida Panhandle before being overcome by a ridge to the West and North and then shooting North East across the Eastern U.S. Those forecasts held and held, and now have come true, with the system only a few hours away at the most from making a landfall near Panama City, Florida.

Official forecast track via the National Hurricane Center with observations down the bottom.

 

 

There have been some monster hurricanes during October in history, including the strongest ever Atlantic system, Hurricane Wilma, back in 2007. So to see such a strong system in what is definitely the latter part of the season and certainly out of the peak, isn’t unheard of. However, this shouldn’t deter from the fact that Michael is a very high end Category 4 system and may even reach Category 5 strength just moments prior to landfall (which may not be indicated on official observations due to the timing between updates from the National Hurricane Center, but it may be reflected by chasers who intercept the eye). 

 

While there is certainly some complacency surrounding what happened with Florence, Michael is a much different story. Michael is an intensifying system which will reach its peak intensity ON landfall, not a day or more prior. This may also enhance the damage near the centre of the system (as seen in previous systems such as Hurricane Harvey last year). The system is likely to bring a life threatening wind threat to not only areas immediately surrounding the landfall region, but extending well inland as it takes the system up to 24hrs to drop back below very destructive wind criteria. Winds of up to 260km/h sustained are possible with this system and 230km/h+ are likely, along with much stronger gusts. There is also the threat of a catastrophic and life threatening storm surge of up to 14ft along the Northern Florida Coast and North East Gulf of Mexico. This storm surge will also extend well inland and completely inundate houses along the Coast which have very little protection from break walls or sand bars. The combination of these two threats will not only pose a significant risk to human life and lead to an obvious state of emergency, but it will also bring down powerlines, completely destroy any buildings near the eye landfall and significantly damage buildings an extensive distance away from the eye, but also bring down trees, lead to excessive flooding and impact communications which could lead to some areas being isolated and stranded for several days. 

Storm Surge Forecast map showing 9ft+ of surge in red, 3ft+ in yellow. This is mostly occurring East of the forecast landfall due to the onshore winds and Coastal bend. Image via the National Hurricane Center.

 

Thankfully the one “good” threat is that the system is fast moving and will likely produce torrential rain, but not excessive rainfall like Florence or Harvey. Heavy rainfall of 100-200m is likely surrounding the core of the system which will extend through Georgia and the Carolina’s, and of course lead to flash flooding and some river and creek flooding, especially through the Carolina’s who have only recently (in the last week or two) seen flood waters ease from Florence. 

Hurricane Michael Rainfall forecast via Windy. Red >100mm, purple >200mm.

 

 

1 08, 2018

NSW Drought: More than 500mm below average, 20mm total for 2018

Its really easy to see how the drought has been exponentially sped up across NSW and parts of Victoria over the course of 2018. The majority of both States is sitting not just below average, but phenomenally below average and its been the epitome of a failed storm season and horrific Winter.

 

Initially when you look at the map, the East Coast of NSW and Eastern parts of VIC stand out. The rainfall deficiency is horrific. The Tweed and Wollongong are down around 400-500mm on average. A normal year, a healthy year would give Bellambi Point near Wollongong a respectable 771mm across the first half of the year, in 2018 that number is a mere 328mm. Its the Coffs Harbour / Dorrigo region that has the greatest deficiency with some areas being more than 500mm below average and localised spots no doubt even greater than that. Greater Sydney for the most part is around 250-350mm below average… a normal year would yield 830mm roughly, 2018 has produced just 503mm in Sydney City.

These rainfall deficiencies seem massive, and they are, but these locations all have 1 thing that Inland NSW doesn’t have, and thats rainfall. Most places along the East Coast of NSW have seen 200-400mm, some higher. That at least fills tanks and keeps the ecosystem running. Yes it will look dry, but there is still water coming out of the tap and dams are at least at a reasonable level (not great, but reasonable).

 

Try Inland NSW… this is clearly the combination of not only a failed and abysmal storm season turning into an endless heatwave as well as a normally consistent rainfall pattern during Winter going completely missing as the fronts move across produce zip. While the maps show a lower deficiency, thats merely due to the averages being far lower. Thats when you need to look at the actual totals.

The following averages are based off the most recent data from January 1st to July 31st, with the totals being valid during the same time period in 2018:
• Fowlers Gap – Average of 167mm, grand total of a mere 7.0mm. There hasn’t been more than 5mm on any given day since July 31st 2017, more than 1 year ago now. The 7mm has come out of 11 days of rain… that doesn’t even darken the dust, let alone settle it.
• Broken Hill – Average of 149.6mm, grand total of just 18.4mm. 
• Menindee – Average of 134.2mm, grand total of 19.3mm across 13 rain days.
• Cobar – Average of 219.4mm, total of just 26.6mm.
• Smithville on the NSW / SA border – No average, but only 30mm for 2018.
• White Cliffs and Wilcannia (towns that recorded as many 45ºc days as anyone during Summer), both only 34mm compared to the average of 187 and 194mm respectively

 

What about Northern and Central Inland NSW, these areas have arguably suffered the most and thats where so many requests are coming out for immediate help. Dubbo, Parkes, Nyngan, Coonamble, Gunnedah, Tamworth all average over 300mm in a normal year, yet are suffering through a horrific total of 75-125mm for 2018. Places like Coonabarabran and Woolbrook average over 400mm with less than 150mm recorded. 

You can say the drought has been around, you can say these Inland places are normally dry… but how does a farmer, a property owner, someone who runs feed lots and is a part of the farming life, how does someone like that see a long range forecast for near normal rainfall – i.e. the rainfall averages listed above, and then need to scramble because less than 30% of that normality has been delivered across 6 months! Nobody can prepare for normal and survive that kind of reality. Nowhere that averages nearly 400mm in half a year, should expect less than 100mm in the same time frame. Its a perfect illustration of how a bad problem was made catastrophic before our very eyes!

NSW VIC 2018 RAIN DEF

16 07, 2018

Its -10ºc, Wheres the snow?

Over the past several mornings as large parts of NSW, Northern VIC and Southern QLD have frozen in one of the harshest cold snaps (for minimums) we’ve seen in the last 5 years… if not longer. Many people have come to us asking where is the snow? or, why isn’t it snowing? we’re seeing temperatures of -10ºc – wheres the closest snow?

While its accurate to associate cold with snow.. the requirements for the temperature to plummet are actually a massive hinderance for snow to occur. Its usually the same process time and time again for these massive cold snaps to occur. A large, slow moving, high pressure system will dominate the region in question (whether thats South East AUS, NSW, Southern QLD, Inland AUS.. it doesn’t really matter). This high will bring clear, cloud free skies along with very light winds and an abundance of dry air – whether its at the surface or just above the surface. This combination allows for all the heat of the day to escape and the temperature to plummet. The light winds allow for dew to set as frost with no disturbance and we wake up to blue skies, white lawns and frozen taps. 

A slice of the atmosphere from this morning (Monday, July 16th) at Glen Innes. You can see a massive amount of dry air dominating the atmosphere with 0% cloud coverage - this equates to absolutely no snow, but frigid temperatures. - Image via BSCH

A slice of the atmosphere from this morning (Monday, July 16th) at Glen Innes. You can see a massive amount of dry air dominating the atmosphere with 0% cloud coverage – this equates to absolutely no snow, but frigid temperatures. – Image via BSCH

 

For a snow event to occur, while the actual daytime maximums are most likely colder… the nights are nearly always warmer than whats experienced in these cold snaps. For snow to occur, you need precipitation. That means you need moisture in the atmosphere which also creates cloud coverage. The cloud coverage traps any heat from coming in during the day (thus why Guyra can have 2ºc maximums sometimes), but also stops any heat from escaping. So the temperature will sit between about -3 and 3ºc for the majority of the time. The increased moisture allows rainfall to occur which in the right conditions will turn to snow. 

Slice of the atmosphere for Wednesday morning, July 18th, which is favourable for Snow over the Tasmanian Highlands... and possibly even some big snow flakes. - Image via BSCH

Slice of the atmosphere for Wednesday morning, July 18th, which is favourable for Snow over the Tasmanian Highlands… and possibly even some big snow flakes. – Image via BSCH

As you can see, the process for either a severe frost or snowfall is virtually completely opposite. Even for the Snowy Mountains its quite rare to see snow falling when the temperature drops below about -7ºc, for the Northern and Central Tablelands of NSW and into Northern VIC and Southern QLD, it would almost never happen as the region doesn’t normally get that cold and therefore it NEEDS the clear skies for heat to escape. 

11 05, 2018

Record Shattering Rain hits Hobart overnight!

Posted 11/5/18 Hobart has been dealt a rapid blow overnight as intense / severe thunderstorms lashed South East TAS record breaking heavy rain and dangerous flash flooding. Above image via Weatherzone showing the 3 main totals (Hobart, Mt Wellington & Grove).

 

 

During Thursday night (last night), a cluster of intense or even severe thunderstorms moved across South East parts of Tasmania. Hobart was right in the cross hairs of the heavy rain which persisted for hours and lead to the City recording its 4th wettest day in history with a staggering 129.2mm – only the 5th time ever Hobart has exceeded 100mm in a day and the first time for May. The rain came down fast with 44mm recorded in the space of an hour (this alone almost broke the May record of 47.6mm at Ellerslie Road). Streets turned into rivers as the Hobart Rivulet broke its banks. This allowed the situation to escalate further as cars were washed down streets and thousands of properties and businesses lost power. The 129mm total is almost 3x the previous May record and 3x the running May average.

 

TAS 11pm Radar

Weatherzone radar as of 11pm showing the intense cluster of storms over South East TAS and Hobart City

 

 

While the system was supposed to be beneficial for snowfall on Mt Wellington, the opposite has occurred with an insane 234.8mm being recorded between 9am Friday and 9am Saturday, this is an all time record for any day – surpassing 202mm set on December 19, 1995. Nearby Grove recorded 158.8mm also which was 2.5x the May record of 60mm and higher than the April 23, 1960 all time record of 154.7mm. This is only the 2nd month (April being the other) that Grove has recorded 100mm+ on a day in.

Other big totals include: Leslie Vale (222mm), Crabtree (143mm), Cannells Hill (131mm), Styx Waterfall (124mm), Nugent (123mm), Buckland (121mm), Sudbury (119mm), Mount Lloyd Road (115mm), Kingston (110mm) – all of which are likely to be at least a new May Record if not for some, an all-time daily record. Maria Island, East of Hobart, also recorded 91mm which was a new town record for May. Hartz Mountains in the South, despite only having records back to 1996 absolutely smashed the 28.6mm record for May with 86mm!

 

Rainfall totals across South East TAS via BOM

Rainfall totals across South East TAS via BOM 

 

 

Conditions are forecast to remain wet and windy at times throughout Friday, but they should begin to ease as the day progresses. So thankfully, unless something unsuspecting happens, the worst appears to be over.

 

OCF Forecast Rainfall for Friday across Tasmania showing rain easing over the South East and increasing over the North East. Image via BSCH / OCF

OCF Forecast Rainfall for Friday across Tasmania showing rain easing over the South East and increasing over the North East. Image via BSCH / OCF

 

17 10, 2017

Fog Formations in South-East QLD & What causes them

Fog is essentially cloud on the ground which reduces visibility to less than 1km and is often referred to as “pea soup”. There are several different types of fog, including radiation fog, advection fog, valley fog, upslope fog, sea fog and freezing fog. All types of fog are able to be visually seen once formed and all have one common effect which is to reduce visibility, in some cases down to less than 50 metres. Thick fog creates hazardous driving conditions and greatly affects other modes of transport such as aviation and boating. In this article we will look at the 4 most common types of fog which occur most frequently during the Autumn and Winter months in the South East Queensland region.

 

 

Radiation fog covers larger areas forming during the night and early morning when there are clear skies and calm winds. There has to also be high humidity and surface air temperature needs to cool to within 3ºc of the dew point. Ground surface heat which has built up during the day quickly cools after sunset with heat being released back into the atmosphere. As the earth cools the layer of air just above the surface also cools but it cools quicker than other air a bit higher up which causes the bottom layer of cool air to become trapped. The trapped air near the surface continues to cool nearing the dew point or 100% relative humidity then water vapour condenses into tiny water droplets and fog is formed. When sun rise occurs the trapped cool air and fog layer near the surface begins to warm causing a reversal in the process. Fog will tend to rise, lift and “burn off” as the surface air is warmed further, air temperatures in the lower atmosphere and surface are equalled out while the dew point seperates causing the fog to evaporate.

Radiation Fog

Radiation Fog

Radiation Fog photo credit James Chambers

Radiation Fog photo credit James Chambers

 

Valley fog is concentrated into smaller areas between hills and mountains during the night and early morning which can occur more frequently than radiation fog due to local environment assistance. The principles of valley fog formation remain the same as the radiation fog process however due to cold air being more dense than warm air it sinks down the surrounding slopes concentrating into low areas. This is known as cold air drainage which feeds in extra amounts of cold air from surrounding higher elevations down into the valley where there is less escape.

ValleyFog

Valley Fog

Valley Fog

Valley Fog over Baroon Pocket Dam. Photo Jeff Higgins 

 


Upslope fog occurs on higher elevations and ranges at any time of day or night. This type of fog forms when warm moist winds (Easterlies in our case) are forced up the slope of a mountain. As the air mass rises higher up the slope, the air pressure lowers, the air expands, and it cools to reach its dew point causing condensation and fog formation. Upslope fog can be long lasting during daylight hours especially if there is cloud cover above to block the suns heating. Locations along the Great Dividing Ranges such as Toowoomba are most prone to these types of fog.

Upslope Fog

Upslope Fog

Upslope Fog and Valley Fog

Upslope Fog and Valley Fog over Mt Tamborine. Photo Jeff Higgins 

Lake fog also known as steam fog occurs over lakes, dams and rivers where the water temperature is much warmer than the air temperature. Water vapour rises from the warm water surface then once becoming mixed with, and rapidly cooled by surrounding air, it condenses into tiny water droplets forming fog. Light winds and a large temperature difference is required for the development of this type of fog which mostly occurs at night or the very early morning. Interesting to note that due to phsyics the fog will never be allowed to reach the water surface!

Lake Fog

Lake Fog at Coolmundra Dam. Photo Jeff Higgins. 

17 10, 2017

Can Hail occur at night?

Its a common conspiracy that hailstones or hailstorms cant occur at night. Why this conspiracy has come about is unsure, it could be from the lack of hailstones people see, who knows… But this will answer that question and explain a bit about it.

Hail hitting Inverell after dark in October 2017 via Ali Marree

Hail hitting Inverell after dark in October 2017 via Ali Marree

 

The short answer is yes. Hail does without a doubt occur at night. I myself have chased several hailstorms after dark in Australia, and countless ones in the States – where I have even been under tornado warned Supercells at 2am which were warned for tennis to softball size hail! So from my own personal account (Thomas) I can assure you, hail does occur at night. That along with the thousands upon thousands of images and videos sent into Higgins Storm Chasing each year showing hail at night.

Its a bit of a mystery as to why people believe it doesn’t happen, but there is some science which can support people’s beliefs to a degree, but also explain the hail production process.

Hail West of Coolgardie, Northern NSW via ABC News

Hail West of Coolgardie, Northern NSW via ABC News

 

 

Hail occurs as water droplets are suspended above the freezing line, within the thunderstorm’s updraft. As time progresses, these water droplets freeze and as time continues… the stones grow bigger and bigger until the updraft’s strength can no longer maintain the weight of the stone. Thats when they fall down to Earth. A key characteristic of a thunderstorms updraft though is heating.. heat and humidity are key ingredients in making thunderstorms, however once the sun drops below the horizon… that heating element soon becomes non-existent and thunderstorms require other means to replace that heating process. The less heat, the weaker the updraft strength and overall cloud height. The lower the clouds, the smaller the area is below freezing (0ºc) within the thunderstorms updraft. The smaller the area, the less hail potential there is. So to a degree, some people may be thinking along those lines and while there is some merit in that argument… Hail (and large hail for that matter) does still occur. The thing is, day and night really have nothing to do with hail… hail is solely reliant on the updraft strength of a thunderstorm and the freezing potential within that thunderstorm (or the energy within the frozen air) – as long as those attributes are occurring, then there is no reason hail cant occur, especially within severe thunderstorms.

Illustration of how hail forms via NOAA

Illustration of how hail forms via NOAA

 

 

16 10, 2017

What are Microbursts?

Microbursts and macrobursts are potentially one of the least understood threats that regularly occur through the Australian Thunderstorm Season. By definition, they are both the same, there are just some very minute characteristics which differ between the two. Microbursts are essentially the more common of the two. So what are they, how do they occur and what are their threats?

 

 

Microburst over Phoenix, Arizona in July 2016 via Jerry Ferguson

Microburst over Phoenix, Arizona in July 2016 via Jerry Ferguson

What are they?
Microbursts and macrobursts are very intense downdrafts that occur within severe thunderstorms and supercell thunderstorms. These downdrafts surge from the clouds, down to the surface where the winds then hit the surface and spread out in a 360º fashion. The ferocity of the wind likely exceeds the damaging threshold of 90km/h, and its a strong reason for many thunderstorms becoming severely warned despite their tame appearance. Essentially… while the winds may seem tame, the conditions are favourable for a microburst or macroburst to occur at any moment. Stronger microbursts and macrobursts can exceed 125km/h winds (destructive criteria) and can even mimic the damage caused by tornadoes.

 

 

There are different forms of microburst’s and macroburst’s bursts also. You can have dry ones, which are far more common through inland parts of Australia and wet ones, which are far more common closer to the Coast and where high levels of tropical moisture are present. Dry ones typically resemble pure wind while a burst of very intense, frequent lightning may also occur near the its taken place. Wet ones of course have the wind, but are also accompanied by very heavy, potentially torrential, bursts of rainfall which will likely cause localised flash flooding. With wet micro/macro bursts, the visual appearance can resemble a rain bomb dropping out of the sky. 

 

Credit: Peter Thompson who sent these photos into Higgins Storm Chasing in January 2015 of a wet microburst occurring 80km North-East of Roma

Credit: Peter Thompson who sent these photos into Higgins Storm Chasing in January 2015 of a wet microburst occurring 80km North-East of Roma

What are their threats and characteristics?
Microbursts:

  • Usually less than 4km in diameter (about the size of a typical suburb)

  • They last up to 15 minutes with maximum intensity lasting between 2 and 4 minutes

  • Winds of 90-125km/h are common and in stronger ones, winds may easily exceed 150km/h!

  • These winds can down trees and powerlines, unroof homes and push cars off the road / highway. Stronger ones may also cause further more significant damage to homes and buildings while being able to push large trucks off highways. 

Macrobursts:

  • Usually larger than 4km in diameter

  • They can last for more than 15 minutes, but typically are less than 15 minutes also, with peak intensity lasting up to 5 minutes

  • Winds of 125km/h+ are usually likely, with peak winds potentially reaching 215km/h!

  • Macobursts have the ability to cause significant widespread damage due to their (by nature) stronger and larger size. They have the ability to cause tornado-like damage with buildings suffering significant structural damage, powerlines and trees downed, cars and trucks potentially rolled or blown off highways. 

16 10, 2017

What is a Landspout?

The term landspout is only a fairly new terminology in the weather world after it was introduced in 1985. The definition of a landspout is a tornado that isn’t associated with a mesocyclone, so by definition… yes landspouts are tornadoes, they are part of the tornado family, however their mechanics are just slightly different in how they form.

 

Landspout near Lara, VIC via Dave Evans (May 2007)

Landspout near Lara, VIC via Dave Evans (May 2007)

 

Landspouts are typically weaker than tornadoes which are produced by supercells and are much harder to detect on doppler radar imagery as the mechanics don’t usually produce a hook-echo on radar, although a weak couplet can sometimes be detected – especially in stronger landspouts. Landspouts are usually as stated above, much weaker than your typical tornado with a rating of EF-2 or less on the Enhanced Fujita Scale although stronger landspouts may reach EF-3 strength. By definition of the EFS (Enhanced Fujita Scale) EF-2 strength is capable of bringing down large trees and unroofing homes and businesses or severely damaging less sturdier buildings such as caravans. 

Landspout observed near Brisbane Airport on March 17th 2017 via Matt Houston

Landspout observed near Brisbane Airport on March 17th 2017 via Matt Houston

 

A unique characteristic of landspouts is that they normally have a translucent tube and they are virtually identical to waterspouts with the only difference being one is over land and one is over water. Not all landspouts are visible, and it usually takes the inclusion of dust, dirt, loose items such as leaves and debris to make the tube become visible. Due to this, they can often be misinterpreted for dust devils however there is the difference that landspouts develop under unstable, showery or stormy conditions where as dust devils develop over more unstable and heat-oriented blue skies.

Landspouts aren’t exactly uncommon in Australia and many tornadoes can be often misinterpreted for landspouts as the differences from a visual perspective can be so minute.

Landspout tornado observed near Cummins, SA in March 2009 via the ABC

Landspout tornado observed near Cummins, SA in March 2009 via the ABC

 

16 10, 2017

What is a Rain Shadow?

Rain shadows are related to and caused by orographic lifting. The process causes the opposite effects of rainfall by orographic lifting, on the opposite side of the mountain rain and as a result, rain shadows are renowned for producing some of the driest climates on planet Earth. Luckily, Australia doesn’t experience harsh rain shadow and this is largely due to the way our Country is shaped, however we do still experience them and in more ways than one.

 

So what are rain shadows, how do they occur and how do they impact Australia?
A ‘rain shadow’ is the dry area on the leeward side (the side away from the wind) on a mountainous area. The orographic lift effect forces moisture up one side of the mountain, where it then cools and condenses on that same side. A rain shadow occurs when this takes place and the mountains whilst producing rainfall also block rainfall from occur on the other side and therefore the name “rain shadow” is adopted as the mountain is casting a shadow of dryness over one side of the mountain. The leeward side of the mountain can also be remarkably hot as the sea breeze becomes blocked and humidity levels plummet. 

Illustration of how a rain shadow works

Illustration of how a rain shadow works

 

 

Rain shadows are renowned globally for producing some of the driest areas on the planet, and while the list is far too long to describe every single one of them.. there are some highlights from the list which are remarkable.

  • The Himalayan Mountains contribute to arid conditions across Central Asia including the Gobi Desert in Mongolia

  • The Arakan Mountains in Myanmar create a phenomenal difference… 750mm of rain occurs annually across Central Myanmar, whereas on the Rakhine Coast (the opposite side of the Mountains) more than 5500mm of rain occurs annually

  • The Judaean Hills in the Middle East are responsible for the Judaean Desert, Dead Sea and the Western slopes of the Moab Mountains. 

  • The Atacama Desert in Chile is the driest non-polar desert on Earth due to the Andes Mountains blocking moisture

  • South-Western parts of Hispaniola, Cuba and Jamaica are in the rain shadow of the trade winds and can receive less as little as 400mm per year compared to the North-Western sides who see more than 2000mm per year and the Highlands who can see as much as 5000mm per year!

  • Death Valley, the worlds hottest location, is located behind the Pacific Coast Ranges and the Sierra Nevada Range. Its the driest place in North America. 

  • Yellowknife, the most populated city in North-Western Canada, is located in the rain shadow of the Ranges to the West

  • San Jose and adjacent cities are usually drier than the rest of the San Francisco Bay area due to the Santa Cruz Mountains 

  • The valley of the Vardar River and south from Skopje to Athens is in the rain shadow of the Prokletije and Pindus Mountains. On its windward side the Prokletije has the highest rainfall in Europe at around 5,000mm with small glaciers even at mean annual temperatures well above 0 °C, but the leeward side receives as little as 400mm.

  • Hawaii may see the biggest rain shadow of the lot, with an entire island in the rain shadow of another island. The island of Kauai records on average, 12,700mm of rain per year due to orographic lifting yet on the Leeward side of the East Maui Volcano, the Island of Kahoolawe is virtually desert. 

    The Tibetan Plateau is probably the best example of a rain shadow around the world

    The Tibetan Plateau is probably the best example of a rain shadow around the world

     

     

There are 4 known official rain shadows within Australia however they arent as significant as those above

  • The Central Midlands of Tasmania receives about 20% of the rainfall than areas West of the Ranges including Mount Read

  • Monaro is shielded by the Snowy Mountains in both VIC and NSW

  • The Western side of Port Phillip Bay in Victoria is shielded by the Otway Ranges. The area between Geelong and Werribee is the driest area in Victoria yet the Otway’s record on average 2000mm per year.

  • In Western Australia, the Great Southern regions are shielded by the Darling Range. Dwellingup records on average 1000mm per year, with Narrogin around 130km to the East of Dwellingup, seeing just 500mm per year. 

So whats the other way we experience them in Australia?
Rain shadows can also be evident through the snow version of them also. While not many areas receive snowfall in Australia, there are some that miss out due to Rain Shadows (or I guess snow shadows in this case). Snowfall occurs down to low levels in Southern Tasmania every year, however due to the way the systems move through, its common for Hobart and more importantly the Highlands of Hobart to miss out. These areas are usually much higher than the forecast snow levels, however Mt Wellington casts a shadow over the region. The same occurs in Canberra where the odd system may produce snow below Canberra’s elevation but the Brindabella Ranges to the West and Snowy Mountains to the South-West cast a shadow over the majority of the ACT and inevitably Canberra. 

Why this occurs is the same process where dry air becomes trapped over the leeward side of the Ranges, so while the temperatures are perfectly adequate for snow to occur not only in those areas, but much lower.. the moisture level is shocking and precipitation struggles let alone snowfall. 

Areas in Australia impacted by Rain Shadows via BOM

Areas in Australia impacted by Rain Shadows via BOM